Mid-latitude weather is largely influenced by processes that redistribute excess energy from the sub-tropics too higher latitudes. It is in the mid-latitudes that warm tropical air masses come in contact with cold polar air masses. Understanding the weather patterns that result from such clashes requires knowledge of weather maps and how they are constructed. The purpose of this lab is to illustrate the construction of weather maps, and to help you identify air masses, fronts, and mid-latitude cyclones on these maps. Surface Weather Maps: Every six hours atmospheric data are collected at approximately 10,000 surface weather stations across the world. This data is used to generate synoptic scale maps that are disseminated to users everywhere. (Synoptic literally means coincident in time and a synoptic map is a map of weather conditions for a specific time.) Since each weather station collects data for as many as eighteen different weather characteristics, a compact method of symbolization must be used to include all of this information on a single weather map. The. station model, developed by the World Meteorological Organization, is the standard format for symbolizing weather characteristics. On the next page you will see an example of the classic WMO station model. Your instructor will guide you through how to read this model. In addition, a complete list of symbols used in the model can be found in your textbook. PAGES 1 AND 2 ARE INFORMATIONAL; READ THEM CAREFULLY, ESPECIALLY THE INSTRUCTIONS ON THE TOP OF PAGE 2, WHICH TEACH YOU HOW TO INTERPRET THE 3-DIGIT GROUP ON THE UPPER-RIGHT- HAND-SIDE OF THE STATION MODEL, WHICH IS THE INDICATOR FOR SEA LEVEL PRESSURE IN MILLIBARS. To decode sea level barometric pressure, follow these steps: 1) Place a decimal point to the left of the last digit. (For example, in the sample below, 147 becomes 14.7) 2) This pressure reading is really a 4-OR-5 DIGIT NUMBER, not a 3-digit number. Next, you have to determine what goes in front-IT WILL EITHER BE A "9" OR A "10." a) If the current number falls between 56.0 and a 99.9, place a "9" before the first digit....OR... b) If the current number falls between 0.0 and 55.9, place a "10" before the first digit. (So, in the example below, 14.7 becomes 1014.7 mb pressure) Cloud type (High cirrus) Total amount of clouds (Sky completely covered) Wind speed (18 to 22 knots) Direction of wind (From the northwest) Temperature in degrees Fahrenheit Visibility (3/4 mile) Present weather (Continuous slight- snow in flakes) Dewpoint In degrees Fahrenheit Cloud type (Low fractostratus and/or fractocumulus) Height of cloud base, (300 to 599 feet) Part of sky covered by lowest cloud (Seven- or eight-tenthe) 34 3/4 32 6 147/ 28 .45 Cloud type (Middle altocumulus) Barometric pressure at sea level. Initial 9 or 10 omitted (1014.7 mb) Amount of barometric change in past 3 hours (in tenths of mb) Barometric tendency in past 3 hours (Rising) Sign showing whether pressure is higher ar lower than 3 hours ago Time precipitation began or ended (Began 3 to 4 hours ago) Weather in past 6 hours (Rain) Amount of precipitation in last 6 hours